Landing in fog

[bigjim996]

Hi People,

Quick question for you:

*Can * all commercial pilots land in fog? I know military can and do. I guess you are all IR rated like militaries are so you *could* but generally don't due to safety reasons...

So what is the visibility threshold, or does it vary due to the technical specs of the various airports??

Thanks for any help..

[rmmonteiro]

hi bigjim996, have you heard about ILS CAT I ; II ; III a) b) c)
it´s all about it.

cheers.

RMM

[Basil]

Yes, we can land in fog, provided that (There's always the small print, isn't there?) :
1. The pilots hold an Instrument Rating (IR)
2. The Ground equipment is suitable, e.g: Instrument Landing System (ILS)
3. The aircraft is ILS equipped.

Category 1. For a manual or automatic landing we require a Runway Visual Range (RVR) - that's visibility along the runway - of 550 metres and must see the touchdown area by a Decision Height of 200 feet.

To go below that we must have autoland fitted.

Cat 2. RVR 350m DH 100ft

Cat 3a. RVR 200m DH 50ft

Cat 3b. RVR 125m DH 15ft

Cat 3c. RVR 75m No DH (As long as the equipment monitors do not pick up a defect we let the aircraft land.)

Military pilots are no better trained for low visibility landing than civil (except for special ops using vision enhancing devices)
We don't avoid landing in fog for safety reasons - with the right kit and training for both pilots and air traffic controllers it's very safe - it's the taxying around in 75m that's difficult :)
Yes, from the foregoing you can see that limits vary according to the level of equipment fitted at the airport and on the aircraft; also if, for instance, any one pilot or flight engineer has not yet completed the low vis ops part of his training on type then the whole crew/aircraft/airport combination will be limited to Cat 1. Undulating terrain close to the approach end of the runway may also affect limits. Some airports have an artificial 'radar floor' of reflectors to give the Radio Altimeter an accurate datum.

Pedant notes ;)
Some airlines have had Cat 2 manual landing using Head Up Displays (HUD).
There may be slight variations to the above figures from airport to airport.

So, what happened to the FR421 STN-PIK last night??? :D

[El Desperado]

Further pedant note :)

Some aircraft are CATII manual-land without a HUD... the ATP springs to mind. Much fun.

[DummyRun]

bigjim996,
just out of interest, which military and what aircraft types do YOU KNOW that can and do land in fog?

[Basil]

<<CATII manual-land without a HUD>>

Ooh er! :eek: - although young Basil allegedly did something like that in an Aztec just after leaving the mil and before he'd worked out that the vis limit now actually constituted an approach ban - duh!

[El Desperado]

And there's more !

Just when you thought it was easy - if the aircraft is not fitted with an auto-rollout system (i.e. to keep it on the centreline automatically after touchdown) such as most DC-10s, the CAT IIIc vis. now requires both mid and stop-end points to have 75m RVR as well.

Previously, you only needed to consider the touch-down zone visibility (runways are divided for visibility measuring purposes into 3 zones - touchdown, mid and stop) but now these other factors come into play.

Basil is absolutely right - it's nothing to do with safety, although low-vis/fog operations are complex, especially if you develop a failure of one system or another (or an engine !) at some point in the approach. That's why we go through it again and again and again and bloody again in the simulator - I suspect most companies have similar training regimes to mine, and I do 10 to 15 practices with all sorts of nasty problems in the sim every 6 months, and quite a few for real on-line.

Basil also forgot to add 'allegedly' to his previous post, so I shall add it for you :cool:

[Basil]

El D - Muchas gracias 4 legal advice. You're retained as my brief :)

BIK - Just shows I don't know everything but I did mention HUDs :p

Cat 3 man land! :eek: :eek:

[FlapsOne]

Just as a point of discussion

I left the military several years ago and, at that time, the vast majority of mil aircraft (maybe all - but I can't 100% sure ) were Cat 1 only. Even the 550m viz limit was raised to 600m for all types.

When the RAF got their first Tristars from BA, the aircraft were Cat 3 capable but I believe the RAF did not train the pilots or maintain the aircraft to keep Cat 3 certification.

I am not sure of the current situation regarding the RAF and Cat 3.

[bigjim996]

Dummyrun,

Re-reading my post, it's badly worded. I don't *know* that they do but am under the impression this happens from chatting to close friends who are RN pilots.

I'll happily accept what you guys say on this one - you're the experts. Me, I fix big computers.

The situation that prompted my question was thus: I was flying into Stansted (Ryanair from Biarritz) on Monday evening and was diverted to Bournemouth :mad: "due to adverse weather conditions" which later turned out to be fog.. Rumour flying around that the pilot wasn't qualified to land in fog and some people were a bit miffed that Ryan Air were using under qualified pilots. I realise this is chinese whispers (and likely rubbish) and should be treated as such but it got me thinking about how you define fog and whether indeed *any*of you guys land in fog and why/why not.

My curiosity is now satiated - thanks. Keep up the good work.

Jim..

PS Where does a 737-800 fit in to this matrix of ILS??

[El Desperado]

I'm sure it was rubbish ! How on earth would the rest of the passengers know if the crew were signed-off or not ?!

I think Ryanair's 737s are CAT II and it may have been the conditions at Stansted were worse than that or the aircraft may have been carrying a defect that rendered it CAT I. Or... the ILS at Stansted had been downgraded, the localiser might have failed, the approach lighting might have been out... who knows !

How do you define fog..... I used to know this... it's to do with the size of the water droplets suspended in the air believe it or not ! At some diameter of droplet mist becomes fog... or is it the other way round. Ahhh... meteorology. Purely a definition, and the real-world application is how far you can see in a straight line through it.

[HEATHROW DIRECTOR]

<<When the RAF got their first Tristars from BA, the aircraft were Cat 3 capable but I believe the RAF did not train the pilots or maintain the aircraft to keep Cat 3 certification.

I am not sure of the current situation regarding the RAF and Cat 3.>>

Many, many years ago at Heathrow we were severely clamped out one evening with no civil traffic flying - before the days of CAT III. An RAF VC-10 had flown in a VIP earlier in the day and called for start-up to return to his base (Brize I think). RVR was about 50m so I asked him what was his minima for take off. He rather sniffily said: "I don't have a minima"... taxied out and took off! Nothing else moved the rest of that day/night.

[shaky]

Heathrow Director

It's True. When I was in the RAF many moons ago there was no prescribed minima for departure. If you could find the runway you were expected to go. We used to take off "under the hood" in training and it was a requirement to be able to demonstrate this for a "Green" or "master Green" instrument rating.

[almost professional]

if the visibility is less than 1000m then its fog, 1000m to 5000m its mist (providing the relative humidity is more than 95%)

[quid]

BJ96-

It may also have to do with the rules for that particular pilot. In some states, you have to have a prescribed number os hours, either in the PIC position and/or hours in that type to go to the lowest minimums. He might have been the world's best, but until he had 100 hours in type, he might be classified as "High Minimums" and not be legal to shoot the approach.

[FlapsOne]

When I was in the RAF the only requirement for take off was 'sufficient visibility to keep straight on the runway'.

I can't remember whether it was written down as a rule, but the guidline was 6 runway lights.

The absolute landing minima were 200' and 600m - no exceptions (except in a war when the rule book went out of the window!!!!!!!!!)

[El Desperado]

The snag with barreling down the runway in extremely low vis is the dreaded RTO at or near V1.

It's ok for the aircraft with virtually centre-line thrust (e.g. VC-10 or pretty much any fast-jet), but once you're talking about aircraft with pods on the wings... well.... it would take a crew with bigger beachballs than I've got !

Almost guaranteed to come hurtling off the side of the runway. Erk. But back then men were men and guys used to fly Canberras home at the weekend :)

Sometimes a tricky consideration - do you de-rate and spend longer on the runway, or ramp up the thrust and have a bigger assymetric problem if one does die on you...

[152captain]

Cat 3b. RVR 125m DH 15ft

Excuse the question, but what is the point of having a DH of 15ft?
Surely, you can't possibly decide to go-around, then actually go-around without losing 15ft? Correct me if I'm wrong (often the case!).

152

[Basil]

It's accepted that the wheels MAY brush the runway on the go-around.

- next Q: 'Wot if the reason for the GA is that we aren't lined up wi' t' tarmac?' :confused:

[FlapsOne]

152

Remeber a DH is not a 'No Go below ht'. It is the height you make the decision at.

El Deperado

I have a couple of thousand hours on the dear old Canberra. I still have thigh muscles the size of tree trunks!!!!!! (nothing to do with my diet).

[Fil]

Basil

When I went through OATS we were taught:

CAT 3b was 75m RVR and No DH (minimums)
CAT 3c was 0 RVR and 0 DH

but would need some method of using instruments to taxi all the way to the gate as with 0 RVR you ain't seeing anything at all. Hence why it is never used in reality.


152 Captain

Now I'm in the real world, on the A319/320 the aircraft can fly to

Cat 3B WITH a DH, in our case 25ft
or
CAT 3B NO DH, ie 0ft

The Performance manual states the lowest limits that we may use for every airport we visit as some only allow Cat3B WITH DH.

The reason in our case for the 25ft limit is that if a go-around is initiated below this height the aircraft may contact the ground (think of a bounce), so it would not be sensible to have a DH below this value unless it is 0 DH (ie the main wheels would be on the ground before you saw anything).

For info, our A319's and A320 CFM's used to be 17ft DH, the 25ft limit got introduced when we added A320 IAE's which for some reason had a higher DH, and the company wished to be consistent so took the most limiting case. All the aircraft can land to 0 DH if allowed to.

[NorthernSky]

Oh dear! oh dear!

Having now summoned Mrs NorthernSky to bring my cocoa and 'special pills', I shall attempt to put a few records straight:

(i) HUDs are marvellous. You can do all sort of things with them which appear impossibly dangerous until you train and try. Manual Cat3a is one of these. (Shooting people down is another!)

(ii) Some aircraft have difficulties with manual landings off Cat 2 approaches, such as B737 300-900 non-Cat3b. This is down to the autotrim, which is the system Boeing had to fit to get around their totally inadequate flight control systems when autoland came in. Future aircraft will have a reasonable system with rollout guidance etc. allowing Cat3b.

(iii) Some aircraft place different relative weightings on different inputs. For example, at Leeds (sloping ground on approach) the B737 can autoland to Cat 3a because it pays little heed to the RA and delta-RA (this is why it floats like a liferaft in the flare for an autoland), whereas the Fokker 100 can only do Cat 2 manual landings because it pays more heed to the aforementioned (which, in turn, is why it greases on most of the time if you let it do its beautiful thing). Allied to this is that many Boeing pilots muck about with the Thrust Levers in the flare when autolanding. Not necessarily a good idea...

(iv) Cat 3b only has a DH if the aircraft can't manage without it (more complex than this of course, but to state a DH for Cat3b is wrong).

(v) Even off a Cat 3a approach with DH 50ft RA you may well touch down during a go-around. That's life, and the experts tell me it won't kill me. Which worries me, because they keep telling me that I'm one if them, and I can only guess!

(vi) Cat 3c is dead and gone because taxying is so tricky.

ps All this talk of the wonderful Fokker makes me wonder whether I shall ever fly one again - anyone needing a pilot for a big and beautiful pencil-jet? That wing, those controls, the not-having-to-bother-putting-flaps-out-for-take-off...

[scanscanscan]

Why have a decision height?
IMHO its a legal thing.
If the pilot does not have a decision height at which to decide to land or goaround who are you going to blame if it ever goes wrong?

[FlapsOne]

Same person you blame if it goes wrong on a visual approach!

[batty]

Bigjim:All airline pilots are qualified to land in fog. Its the thickness and density of the fog that governs if the pilot can land. There are lots of ifs and but though.....

As a pilot progresses as a pilot he/she can take further qualifications that allows him/her to land in thicker fog. These greater qualifications are called Cat II and Cat IIIa,b,c . Cat IIIc basically allows the pilot to let the aircraft land itself in virtually impeniterable fog.

Even if the pilot is qualified up to CatIII they can only land to the limits of the lesser rated pilot on the flight deck. ie if one pilot is Cat II and III and the other is only Cat II the flight is limited to Cat II minima.

Even if both pilots are Cat III, if the aircraft has a minor defect it can result in the aircraft not being Cat III able.

As a final point the airfield itself has to have been tested and cleared to a specific Cat level.

As a final point the Ryanair aircraft are generally cleared to Cat IIIa and the crews are mostly trained to that level, unless very new to the airline. Your diversion to Bournemouth could have been due to a multitude of reasons. I was flying that night and both myselft the captain and the aircraft were all Cat III and landed twice no problems.

[Lump Jockey]

So why not equip all a/c with CAT IIIc equipment? Is it bigger physically to install? And is that true that if one of the crew doen't have the required qualifications, then the aircraft diverts? Sounds well weird that! Obviously it's a rule for some reason or another though. Are full autolands a bit....well, you know.....SCARY?!:(

[batty]

Lump Jockey: It would be great to equip all the aircraft with CatIIIc equipment, however different aircraft of different generations ie 737-100 and 737-800 have different though similar systems, even within the same generation depending what was specified by the original purchaser. Think of it like buying a car , you have all the options for all the toys from new, depending on you budget, but if you buy secondhand you take what you get. Its not just a matter of slapping in a 'CatIIIc box'. To make the aircraft C3c would involve changing many many components and avionics systems, and in the end would be hugely expensive for the one or two occasions in the year when it is needed.

Yes if one of the pilots isnt qualified the aircraft will divert. Flying as a whole is covered by a multitude of backup systems. What would happen if something went wrong very late and low on a C3 approach , ie the qualified pilot collapsed? Also the approach isnt just flown by one of the pilots it is flown by both, generaly the First Officer (F/O)will fly the aircraft on instruments to the decision height ie 50ft (or lower) whilst the Captain monitors the approach and looks out the window. At decision the F/O calls decide and the Captain will say land, if he can see the runway and takes control whilst the F/O remains on instruments, or he will say Go around and the F/O will fly the go around. Its not a one man band!

Hope that explains things a little better....

[Jetstream Rider]

I fly the Jetstream 41 and we have a limit of 100ft and 300m (with no requirement for any RVR in the mid and stop end) for a Cat 2, which is always a manual landing as our autopilot cannot land the aircraft. The other night at Leeds, we did at Cat 2 with a 10 knot tailwind - we can accept that on 32 (which is the only Cat 2 runway at Leeds) as we are small and it doesn't take us ages and ages to stop. The Jets however cannot, so they all went to Manchester or Teeside! Ho ho! We were the only commercials that got in.

For our Cat 2's the Captain flies the approach in Auto and the First Officer monitors the instruments. Captain looks out from 100 above decide and First Officer keeps heads in. Auto is disengaged at 80 ft, Capt looks out and FO keeps looking in giving advice if there is any deviation. I have only flown a couple down to real minimums, but I quite enjoy it. Very surreal when a few runway lights slowly appear a few seconds before landing.

[Lump Jockey]

I'm not a pilot, no where near it. But I do enjoy aviation and would have loved to have been a pilot! The reply I got there from batty was awesome, and a new appreciation of your fabulous job, I now have!:) Sounds great!:D

[682ft AMSL]

Particularly interested in the comments of those who have clearly experienced the 'joys' of Leeds on a foggy day. The installation of CAT3 on 32 has made things better than in the past, but as J-Rider and Northern alude to, the slope & the seemingly everpresent tailwind seem to limit its usage to everything other than J41s, 146s and empty Embraers!

The question is, what can be done to improve matters. Can the CAT3 system on 32 be improved? If so, how? Is manual CAT2 possible on 14 with the 3.5 degree glide. The ability to get in with a 300m minima on 14 would elimate the majority of the current diversions.

Comments appreciated.

682